1. Technical Field
The present invention relates to a method and apparatus for testing a head gimbal assembly and to a head gimbal assembly. More particularly, the present invention relates to the use of a laser-based system for testing of a head gimbal assembly.
2. Description of the Related Art
In an assembly or a fabrication of a head supporting arm used in a magnetic data recording device, such as a hard disk drive device, a very small slider, a read/write head is attached, or bonded to a flexure by an adhesive, such as a thermosetting resin. FIG. 1 shows a prior head supporting arm 1 which includes an actuator arm 2 which has a pivot point 3 mounted on a frame of the hard disk drive device, a load beam 4, a mount plate 5 connecting the load beam 4 with the actuator arm 2, a flexure 6 attached to the load beam 4, and a slider 7 mounted on the flexure 6. The mount plate 5 and the actuator arm 2 are coupled by a swaging connection 8. The slider 7, the flexure 6, the load beam 4 and the mount plate 5 are called as a head gimbal assembly (HGA).
A flexible tube 9 containing four connecting wires 10 connected to a read/write head 13, such as a MR head, shown in FIG. 2, on the slider 7 is mounted on one of the side edges of the head supporting arm. The tube 9 is fixed to the side edge at plural positions by fixing elements 11. This type of head supporting arm is used in a contact start stop (CSS) scheme in which the slider 7 is landed on an outer landing zone of the surface of a data recording disk, such as a hard disk, when the rotation of the hard disk is stopped during a standby condition. When the rotation of the hard disk is started to read the data from the hard disk or to write the data onto the hard disk, the slider 7 takes off from the landing zone and flies above the hard disk.
The FIG. 2 shows a positional relationship of a front end of the load beam 4, the flexure 6 and the slider 7. A dimple 12 formed on the back surface of the load beam 4 contacts an upper surface of the flexure 6 to realize a gimbal action of the slider 7. In the assembling process, the flexure 6 is fixed on a back surface of the load beam 4, and the slider 7 is attached on a back surface of the flexure 6 by the thermosetting resin 15.
The cure of the entire thermosetting resin is performed in an oven. Before the heating in the oven, a laser beam is applied in a small area 16 of the exposed area 14 of the flexure 6 to cure the thermosetting resin in the area 16 for tacking the slider 7 onto the flexure 6. This tack is called as a laser tack. Such laser tack becomes possible in the head supporting arm 1 used in the CSS scheme since the portion 16 is exposed in the such arm 1.
U.S. Pat. No. 6,282,064 B1 shows a head gimbal assembly comprised of a load beam, a pair of flexure arms, a slider support member and a plurality of electrical lines. The head gimbal assembly is formed from a laminated material comprised of a support layer, a dielectric layer and a high strength electrically conductive layer.
A variety of other head gimbal assemblies and head stack assemblies is known from the prior art. However, regardless of the type of drive, during operation the disk rotates about its axis, while the actuator arm moves the r/w head across the disk. The actuator arm moves the r/w head to different areas of the disk to allow the r/w head to read data from and write data to the disk. The disk itself is divided into a number of concentric tracks each having the same width. These tracks are in turn divided into a number of sectors. In seeking out a particular track, the actuary head moves in a radial direction from its current location to the location of the track in which the data sector it is seeking is located.
For the r/w head to operate properly, it should perform its function at a distance in the tens of microns above the surface of the hard disk. If the distance between the r/w head and the disk gets too small, if impurities form on the surface of the disk, or if the head moves too much in a vertical direction towards the disk, the r/w head can impact on the surface of the disk, causing damage to the head and the disk. This undesired collision is called a head crash.
In addition, for the r/w head to operate properly, it must also be moved to the desired track and sector of the disk within a narrow horizontal range as well. Too much horizontal displacement can cause the r/w head to be improperly aligned over the desired track and sector. A horizontal displacement of as little as 8 microns can cause the disk drive to fail to operate properly.
An inherent limitation in the read/write process is the fact that the actuator arm and the r/w head will oscillate slightly in a horizontal direction as they move back and forth. Since the r/w head must stay very small margin of horizontal movement when seeking a particular track, the oscillation must be kept to within a very small tolerance. Too much oscillation will result in the very real possibility of an improper alignment of the r/w head during a point of maximum oscillation, meaning a failure to read or write data properly.
In order to ensure upper operation of the hard disk drive it is known from the prior art to measure the gram load which is exercised by the head gimbal assembly onto the disk when the disk is not in motion. In operation the head takes off because of the lift which is caused by the movement of the disk. This way a balance is constituted between the lift force and the gram load such that the head is at a defined attitude over the disk.
This testing method has some disadvantages. One disadvantage is, that the testing cannot be performed in situ but needs to be performed before the assembly of the disk drive. During the assembly process the mechanical properties of the head gimbal assembly can change. Another disadvantage of this prior art testing method is that only the static case is tested but not the impact of dynamic loads which occur when the actuator arm moves the head to different tracks.
U.S. Pat. No. 5,979,249 shows an actuator resonance tester for a disk drive. The tester includes an actuator arm, a pivot, one or more weights, a voice coil, a voice coil motor, an accelerometer, and a processor. The one or more weights are formed on the actuator arm to simulate the mass of at least one read/write head.
The base and the test housing are affixed to either end of the pivot to provide it with proper boundary conditions to simulate the boundary conditions of a fully-assembled hard disk drive device. The voice coil and the voice coil motor move the actuator arm rotationally around the pivot. The accelerometer is placed on the actuator arm to measure the horizontal acceleration of the actuator arm. The processor determines the resonance of the actuator arm based on the arm's measured horizontal acceleration. One of the disadvantages of this tester is that in situ testing is not possible.
WO 01/18 557 shows a method for testing disk drive read/write heads. The testing is performed by writing information to and reading information from a non-disc shaped media paddle that is caused to move back and forth with respect to the read/write head on oscillatory fashion.
In the past, the actuator resonance has been measured through the use of a laser-based testing system, comprising a laser Doppler vibrometer, a digital signal analyzer, a precise x-y-z fixture, and a high-fidelity power amplifier. An example of this conventional method is shown in “Drive Level Slider-Suspension Vibration Analysis And its Application to a Ramp-Load Magnetic Disk Drive,” by Ta-Chang Fu, et al., IEEE Transactions on Magnetics, Vol. 31, No. 6, (November 1995), the contents of which are hereby incorporated by reference.
It is therefore desirable to provide an improved method and system for testing the head gimbal assembly which does also encompass the dynamic case when the disk drive is in operation.